It is advantageous in an AC power transmission system to provide for the transmission at high voltages on the order of 1 kVRMS to 35 kVRMS. For ultimate use by the end user or power consumer these high voltages must be subjected to a down conversion such that a much lower AC voltage is supplied.
In various known arrangements the high voltages are first converted to medium voltages in the range of 1 kVRMS to 35 kVRMS. These medium voltages are then subjected to a conversion process utilizing an arrangement such as that shown in the block diagram of FIG. 1. In such an arrangement the medium AC voltage is converted to a medium DC voltage such as by a rectifier 110. The medium DC voltage, MV DC, is then stepped down to a low DC voltage, LV DC, in a circuit that includes a DC to AC inverter 120, a transformer 130 and an AC to DC Converter 140. The result is a low voltage DC output that can then be used as the input to a module that can comprise, for example, a 3-phase DC to AC converter.
While various arrangements have been proposed for such conversion circuits, each has had shortcomings, particularly as designers have struggled to implement a silicon-switch based solution where the switches that are turned ON and OFF to provide, for example, the conversion from DC to AC, are subjected to enormous stress by the switching transitions that occur at these medium voltages. It would therefore be useful to have a switching arrangement that includes semiconductor-based switching that has sufficient stability to enable soft switching of such switches thereby reducing the stress at the transition points in the conversion process at these medium voltages. Use of passive and active clamping methods in the primary connected circuit for the purpose of limiting voltage excursions, corresponding losses, and device voltage stress typically has yielded a larger number of components with high stress and lower systemic reliability. It would be useful to provide a circuit arrangement that performs voltage clamping on the primary side with higher systemic reliability.
In accordance with an aspect of the present invention a primary to secondary transformer constructed with small leakage inductance allows that various clamping methods may be available on the secondary which are effective in then acting as voltage clamps to the primary circuit and components. Such a method and circuit arrangement described herein effectively performs voltage clamping to the primary side by use of low voltage components on the secondary. The result is higher systemic reliability.